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Re: [Discuss-gnuradio] find_usrps only succeed when an sniffer is ON
From: |
Marcus D. Leech |
Subject: |
Re: [Discuss-gnuradio] find_usrps only succeed when an sniffer is ON |
Date: |
Tue, 07 Sep 2010 11:01:56 -0400 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.11) Gecko/20100720 Fedora/3.0.6-1.fc12 Thunderbird/3.0.6 |
On 09/07/2010 04:43 AM, Jorge Miguel wrote:
> I installed GNU Radio on a ThinkPad Lenovo T4410 under Ubuntu 10.04.
> After connecting the USRP2 with the original Ettus code on the SD card
> D and F LEDs are ok and when executed:
>
> ~$ sudo find_usrps
> No USRP2 found.
>
> I run wireshark or tcpdump to see what happens in my network and I got:
>
> ~$ sudo find_usrps
> 00:50:c2:85:35:a2 hw_rev = 0x0400
>
> If I stop the sniffer, I get again:
>
> ~$ sudo find_usrps
> No USRP2 found.
>
> My problem is that 'find_usrps' only works when a sniffer is running.
> How can it be explained?
>
> Jorge,
>
When a sniffer is running, the ethernet interface is placed into
"promiscuous" mode in which all ethernet frames are processed and passed
up to higher layers in the networking stack. In non-promiscuous
mode, only frames that are addressed to the particular hosts ethernet
address, and the broadcast address, are forwarded up the stack.
My understanding is that find_usrps sends out a broadcast packet, and
the responding USRP2 replies using a broadcast packet, but even
in non-promiscuous mode, the hosts interface should pass the broadcast
traffic "upwards". I wonder if there's some interaction with
firewall rules at play here as well?
--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org